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"Vampire" Night Vision Systems
"Vampire" is the code name given to a number of infrared imaging devices developed by the United States military for improving combat effectiveness at night. These devices take many forms, both man-portable and vehicle-mounted, but all consist of two basic components - an infrared light of varying size and power along with an image converter in the form of either a scope or goggles. The technology behind the Vampire system is still in its relative infancy and operates basically in the same way as normal search light systems, except that one requires a special type of electronic imaging scope to see the beam. "Passive" systems using ambient light without the need for a synthetic infrared light source remain in rather troubled development and are still years from entering service, while thermal imaging devices - that is, optics with the capability to "see" radiated heat in a visual format - remain purely theoretical. The term "Vampire" is derived not only from the supposed ability of such mythical creatures to see clearly in darkness, but from the eerie red light of the infrared lamps. Although the beam from these devices is not discernable to the naked eye, the bulb still emits a non-radiating scarlet glow that can be seen from some distance with a clear line of sight. Infantry Systems M21 "Vampire B" The M21 is the older and more cumbersome of the two man-portable systems, developed for use by snipers. However, the light itself is quite powerful and the system has a range of about a kilometer, making it ideal for taking out targets over great distances. Like all Active IR devices, the lamp produces a visible red luminescence from the bulb of the light, while the beam can be seen and traced by anyone carrying an IR detector or another infrared scope. Fortunately, these devices are quite rare among Russian forces. M30 "Vampire F" The M30 system is a newer, more mass-produced system intended for use by regular infantry forces. Like the M21, it is an accessory for the M14 Battle Rifle, and a second version exists for the Thompson Submachine Gun. The Vampire F system consists of a much smaller and less powerful IR light that is mounted atop the soldier's rifle like a scope, but is off-set from center so that it does not block the firearm's built-in sights. The second element of the system is a pair of binocular-like IR Goggles that enable their user to see the light's beam, although they do not provide the image enhancement effect of a telescopic sight. Both pieces of equipment require a wired connection to a battery pack worn on the soldier's belt. Standard procedure involves issuing an M21 kit to the designated marksman of an infantry squad to provide longer range optical capability, while the rest of the men receive the shorter-range M30. Vehicular Systems M27A2B1 "Vampire D" The Vampire D system is fitted as standard equipment for M77 Personnel Carrier half-tracks. The M27A2B1 kit consists of two M27A systems with battery, 25 cm IR lamp and image converter telescopic sight in a single mounting, fitted to both the forward and rear-facing machine guns. A larger 45cm IR spotlight - M27B - is attached on a gimble to the right side of the half-track's cabin, where the commander sits. The vehicle itself also comes standard with infrared as well as normal visible light head lamps and image converter goggles for each of the three crewmen (driver, commander and forward machine gunner). The Vampire D system remains fitted to an M77 half-track at all times, even during the day, while the crewmen's night-vision goggles are hung on wall brackets next to their headphones and throat mics. M27A2B1-equipped half-tracks operate in support of the infantry squads they carry to provide enhanced capability, forming an integral part of that unit's overall night vision system. M25 "Vampire C" The Vampire C system is a modification of the M78 half-track (a utility cousin to the M77 personnel carrier), mounting a large 70 cm infrared searchlight in the transport compartment behind the cabin. It may be operated either remotely by the vehicle's commander from the right side seat of the driver's cabin, or directly by the machine-gunner who is positioned at the front of the transport compartment. M25 IR-equipped half-tracks were once very important components of the night fighting system prior to widespread introduction of the more advanced M27 "D" and M30 "F" systems, but have since declined in both number and operational value. However, the large effect radius, long range and intensity of this system's IR lights makes it still a valuable asset. The system is also fitted to M57 self-propelled anti-aircraft artillery, and M78 half-tracks equipped with it are usually paired with towed anti-aircraft weapons and 127mm anti-tank guns. M29A3B2 "Vampire E" The M29A3B2 "Vampire E" is the tank-mounted analogue to the M27 "D" system for the M77 Half-track. The M29 system fits an M27A1 system to the loader's hatch machine gun, adds a 45cm IR lamp mounted coaxially above the main gun and another one on the side of the turret that can be hand-swiveled by the loader, plus regular 25cm IR lamps for the driver's hatch and commander's cupola. It upgrades all the sights and periscopes - Commander, Gunner and Driver - to dual-purpose day/night scopes and gives IR goggles to each crew member. Other Derivatives OPTAC Fire-control / OPTAR Rangefinding Systems The M253 Optical Tracking, Acquisition and Ranging, or OPTAR, or OPTAR, rangefinder system is an advanced electro-optical target acqusition system developed for the M155 Heavy Tank (127mm Gun Full Tracked Heavy Tank, M155) from the wider Vampire program's technologies. It has also been retroactively fitted onto the M70 Heavy Assault Gun. This advanced rangefinder is part of the OPTAC (Optical Tracking, Acquisition and Computing) fire-control package and is mounted in an armored cowling on the exterior hull of the equipped vehicle (on the right side of the turret in the case of the M155, or atop the casement on the left side, directly opposite the commander's cupola, in the case of the M70). Essentially, the M253 OPTAR Rangefinder works by emitting extremely powerful pulsed beams of semi-coherent infrared light. This enables the gunner - through the advanced fully-electronic OPTAC ballistic computer - to determine the range to target by timing the reflection of said infrared pulses. A conventional, if unusually powerful, stereoscopic rangefinder is also included in case the information needs to be double-checked by more familiar, tried-and-tested means, but can also be used in situations where the OPTAR would be disadvantageous (since any enemy personnel with infrared image converters would be able to see the OPTAR's light pulses and determine their source). However, despite this potential shortcoming, the advantages of the system are obvious. The limit of normal stadiametric gun sights (which were the sole fire-control mechanisms available to tanks until the mid-to-late 1940s) is 1000km - "marking" one with incrimants out to greater distances is pointless, and firing at targets beyond 1km would require the gunner to shoot purely "by feel". Stereoscopy- & coincidence-based rangefinders, which were originally used for naval guns but began to appear in compact forms on tanks in the 1940s and became commonplace by the end of the decade, still required mental arithmatic on the part of the gunner and were not perfectly precise. They were also rather time consuming to employ, and in many cases tank crewmen still prefer - or are forced - to make shots beyond the ranges of their stadiametric sights by old-fashioned instinct (limiting their practical range to within 2km at absolute most). With the OPTAC package, the need for manual aiming and range determination is eliminated entirely. The M253 optical system can determine the range to target in a fraction of the time required by even a very experienced gunner using the standard U.S. M15 stereoscopic (or newer M24 coincidence) rangefinder - well less than a second. Furthermore, it does not suffer from the 1,000-meters limitation of a simple stadiametric sight. Thus, American tanks equipped with OPAC systems can make accurate kills from distances at which enemy armor would be completely incapable of retaliating. The only practical limitation on the range of the OPAR/OPAC package is the ability of the crew to see, and then aim the infrared emitter at, their target. Terrain features or the curvature of the earth will obscure a hostile vehicle long before the infrared beam will scatter beyond effeciveness. Nonetheless, the OPAC package also has a backup M24 coincidence rangefinder system and the standard stadiametric telescopes equipped with image-converters (from the M29A3B2 "Vampire E" system). The OPAC's electronic FC computer is designed to accept manual input as well; thus, it can be used in conjunction with conventional visual sighting methods to improve aim efficiency even when the OPTAR rangefinder is not employed. Earlier versions of the OPTAR, mounted on expirimental tank designs during the 1940s & '50s, suffered from one major short-coming in particular. They used very powerful, but entirely incoherent, pulses of infrared light: the emitter was essentially just a powerful spotlight with a red-shifting filter over the lens, as found on the Vampire nightvision packages. This resulted in the rangefinding pulses being "scattered" in conditions where the air was saturated with obstructions (rain, snow, sand, etc). Thus, the OPTAC computer would receive multiple range returns and the gunner or commander would have to use a normal visual rangefinder system to determine which of them was correct. At best, this could only result in a slight improvement in sighting times - the crew would be lucky if the returns they received were coherent enough to give them a general idea of the range to look for. The latest M253 iteration - the first OPTAR model to see service production - solves this problem using multiple filtered lenses with ruby matrices to focus the beam, making it more coherent and less susceptible to being scattered. Of course, this also means that the M253 is far too expensive to see general deployment among more common U.S. armored fighting vehicles like the M60 & M65. Development of a more cost-effective OPAR emitter with limited scattering resistance for general deployment is ongoing.